The Ozone Story Revision Flashcards

HideShow resource information
  • Created by: LBCW0502
  • Created on: 07-05-16 20:23
What are the two most chemically important regions in the atmosphere?
Troposphere and stratosphere
1 of 63
What are the the four most abundant gases in the atmosphere?
Nitrogen (78%), oxygen (21%), argon (1%) and carbon dioxide (0.0399%)
2 of 63
How do you convert from percentage to ppm?
Multiply the percentage by 10,000 (for ppm to percentage, divide the ppm by 10,000)
3 of 63
What are the consequences of high exposure to UV radiation?
Can cause a mutation in DNA, skin cancer, irritate blood vessels, cause sunburn, damage proteins within the skin, damage crops etc.
4 of 63
What is the most damaging part of the electromagnetic spectrum?
Ultraviolet radiation
5 of 63
What type of molecules are present in sunscreen?
Benzene rings or alternating double and single bonds (when UV light is absorbed the electrons in the pi orbitals in these bonds are promoted to higher energy levels)
6 of 63
What is the role of ozone in the atmosphere?
To absorb UV radiation from the Sun
7 of 63
Why is ozone an issue in the troposphere?
Ozone is a significant pollutant because it is involved in reactions producing photochemical smog which causes haziness and reduced visibility, irritation and respiratory problems
8 of 63
Why is there no life in the stratosphere?
High energy UV radiation would break down delicate molecules of living things
9 of 63
How do you calculate the speed of light?
Speed of light (ms-1) = wavelength (m) x frequency (s-1)
10 of 63
How are the two theories of light (wave and photon models) linked together?
Energy of a photon (J) = Planck constant (Js) x Frequency (s-1)
11 of 63
What is the value of Planck constant?
6.63 x 10^-34 Js
12 of 63
What do you need to do when calculating the energy value per mole of photon?
Multiply the value per photon by the Avogadro constant
13 of 63
What does the term 'quantised' mean?
(Electronic energy) has fixed levels
14 of 63
What are the different energy changes for different parts of the spectrum? (in order of increasing energy)
Translational energy, rotational energy (microwaves), vibrational energy (infrared radiation) and electronic energy (visible and UV)
15 of 63
What are the three things that could happen to a chlorine molecule when it absorbs radiation?
Release energy and chlorine returns to its original state, dissociation and ionisation
16 of 63
What is heterolytic fission?
Both of the shared electrons go to just one of the atoms when the bond breaks. This produces two ions (an anion and a cation)
17 of 63
What is homolytic fission?
One of the two shared electrons goes to each atom. This produces radicals (they have an unpaired electron)
18 of 63
What is an initiation reaction?
A molecule photo-dissociates (using UV radiation) to form radicals
19 of 63
What is a propagation reaction?
A radical and a molecule react to form a new radical and a new molecule (there is a radical on either side of the equation)
20 of 63
What isa termination reaction?
Radicals reacts to form molecules (radicals are removed)
21 of 63
What is the name of the overall reaction taking place in the atmosphere
Radical chain reaction (or free radical substitution reaction)
22 of 63
What does a full-headed curly arrow and a half-headed arrow show?
Full headed arrow shows the movement of a pair of electrons and a half headed arrow shows the movement of a single electron
23 of 63
What is the general calculation for the rate of reaction?
Rate of reaction = change in property / time taken
24 of 63
What are the five ways of measuring the rate of reaction?
Measure the volumes of gases evolved, measure mass changes, pH measurement, colorimetry and chemical analysis
25 of 63
What five factors affect the rate of reaction?
Concentration of reactants, temperature, intensity of radiation, particle size of solid and the presence of a catalyst
26 of 63
What is the definition of activation enthalpy?
The minimum kinetic energy required by a pair of colliding particles before reaction will occur
27 of 63
What is the name of the graph which can be used to show to distribution of energies?
The Maxwell-Boltzmann distribution
28 of 63
How do you draw a distribution curve when the temperature is increased?
A curve is drawn to the right and lower than the original distribution curve
29 of 63
What is catalyst?
A catalyst speeds up the rate of reaction by providing an alternative route with a lower activation energy
30 of 63
How does the presence of a catalyst affect a distribution curve?
The activation enthalpy is lowered so more particles have enough kinetic energy for the reaction to occur
31 of 63
What type of theory can be used to explain how an increase in temperature increases the rate of reaction?
The collision theory
32 of 63
What is a homogeneous catalyst?
A catalyst that is in the same physical state as the reactants in the reaction. They normally work by forming an intermediate compound with the reactants
33 of 63
What do catalysts not affect in a reaction?
Catalysts do not affect the position of equilibrium in a reversible reaction
34 of 63
Name five examples of radicals
Chlorine, bromine, hydroxyl radicals, nitrogen monoxide and nitrogen dioxide
35 of 63
How do radicals act as homogeneous catalysts?
They go through a catalytic cycle a number of times and the radicals can be regenerated
36 of 63
Why are nitrogen monoxide and nitrogen dioxide radicals unusual?
They are relatively stable molecules and they can be prepared and collected like ordinary molecular substances (not all radicals are highly reactive)
37 of 63
What are the uses of CFCs?
Refrigerants and in air conditioning units, aerosol propellants, blowing agents for expanded plastics such as polystyrene and dry cleaning solvents
38 of 63
Which properties of CFCs did Midgley demonstrate?
The lack of toxicity and the lack of flammability
39 of 63
Which compound did CFCs replace?
Ammonia
40 of 63
What is a polar bond?
One part of a molecule is slightly positively charged and another part is slightly negatively charged (bonding electrons are not shared equally)
41 of 63
What is electronegativity?
A measure of the ability of an atom in a molecule to attract electrons in a chemical bond to itself
42 of 63
What are the three most electronegative elements?
Nitrogen, oxygen and fluorine
43 of 63
What is the trend when the hydrocarbon chain increases (in terms of bonding and boiling points)?
The longer the chain, the stronger the intermolecular forces and the higher the boiling point (more energy is required to overcome the bonds)
44 of 63
Why do straight-chain alkanes has a higher boiling point have branched isomers?
Straight-chain alkanes have more contact between molecules and more intermolecular bonds can form whereas branched isomers cannot be closely packed together
45 of 63
What is a dipole?
An molecule (or part of a molecule) with a positive end and a negative end (polarised)
46 of 63
What is a permanent dipole?
When two atoms have different electronegativities e.g. HCl
47 of 63
Why is there no overall dipole in tetrachloromethane?
This molecule has a tetrahedral shape and the chlorine atoms are distributed symmetrically around the carbon atom (there are polar bonds but no overall dipole)
48 of 63
What is an instantaneous dipole?
Electrons are in a constant state of motion and at a particular instant, they may not be evenly distributed. This would cause a temporary dipole (one end of the molecule has a greater negative charge than the other end).
49 of 63
What is an induced dipole?
An unpolarised molecule is next to a dipole. The dipole attracts or repels electrons in the unpolarised molecule, inducing a dipole in it. The dipole can be induced by a permanent dipole or an instantaneous dipole
50 of 63
What is the weakest type of intermolecular bonding?
Instantaneous dipole-induced dipole bonds
51 of 63
What is the strongest type of intermolecular bonding?
Permanent dipole-permanent dipole bonds
52 of 63
What is the strongest type of intermolecular bonding than can be formed (in the case of halogens)?
Instantaneous dipole-induced dipole bonds
53 of 63
Which halogen forms the weakest instantaneous dipole-induced dipole bonds?
Fluorine has the weakest instantaneous dipole-induced dipole bonds, having fewer electrons and the lowest melting and boiling points of the halogens
54 of 63
What is a chlorine reservoir molecule?
Molecules that store chlorine (in the stratosphere) e.g HCl
55 of 63
Which type of bonding is a special case of permanent dipole-permanent dipole bonding?
Hydrogen bonding
56 of 63
What are the three features of hydrogen bonding?
A large dipole between a hydrogen atom and highly electronegative atom (e.g. oxygen, nitrogen or fluorine), a small hydrogen atom close to an electronegative atom and a lone pair of electrons on an electronegative atom
57 of 63
What are the properties of compounds with hydrogen bonding?
Higher boiling points, high viscosity and often soluble in water
58 of 63
What is the definition of substitution?
A reaction in which one atom or group in a molecule is replaced by another atom or group
59 of 63
What is a nucleophile?
A molecule or negatively charged ion with a lone pair of electrons that it can donate to a positively charged atom to form a covalent bond
60 of 63
Name six common nucleophiles
Hydroxide ion, cyanide ion, ethanoate ion, ethoxide ion, water and ammonia
61 of 63
What are the trends in the properties of the bonds of carbon-halogen bonds?
The bond strength decreases down the group and bond polarity decreases down the group
62 of 63
Which compounds are replacing CFCs?
HCFCs (then HFCs)
63 of 63

Other cards in this set

Card 2

Front

What are the the four most abundant gases in the atmosphere?

Back

Nitrogen (78%), oxygen (21%), argon (1%) and carbon dioxide (0.0399%)

Card 3

Front

How do you convert from percentage to ppm?

Back

Preview of the front of card 3

Card 4

Front

What are the consequences of high exposure to UV radiation?

Back

Preview of the front of card 4

Card 5

Front

What is the most damaging part of the electromagnetic spectrum?

Back

Preview of the front of card 5
View more cards

Comments

No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all The Ozone Story resources »